Conventionally known polarizing films include polyvinyl alcohol (PVA) base films dyed with iodine or a dichroic dye. Since these polarizing films, though exhibiting excellent polarizing performance, are inferior in heat resistance, moisture resistance, and the like, an acetyl cellulose film or the like film has been laminated thereon for practical use. Nevertheless, the laminated polarizing films still have insufficient moisture resistance depending on use.
Polarizing films comprising, as a film base material, a hydrophobic polymer other than PVA have been proposed, in which a vinyl halide polymer, e.g., polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), etc., is dehydrohalogenated to form a polyene structure. However, they have not yet become so popular not only because they are also unsatisfactory in stability to heat, light or oxygen but because a free choice in hue is not allowed.
Further, polyamide base polarizing films have also been proposed as disclosed in Japanese Patent Publication No. 3944/74 and Japanese patent application (OPI) No. 45153/79 (the term "OPI" as used herein means "unexamined published Japanese patent application"). Although the polyamide-dye type polarizing films are superior to PVA-iodine polarizing films, PVA-dichroic dye polarizing films, or polyene type polarizing films in terms of heat resistance, moisture resistance, dynamic strength, and the like, they are inferior in polarizing performance to these three types of polarizing films.